1. Field of the Invention
The present invention relates to an FM stereo demodulator, and more specifically to an FM stereo demodulator to be used in a high fidelity FM receiver circuit.
2. Description of the Prior Art
FM stereo demodulators, used in a stereophonic FM receiver for separating left and right signals from an AM-FM composite signal (FM detector output signal) are divided into several types.
Among those prior art demodulators, a switching type FM stereo demodulator is popularly used. In the switching type demodulator, left and right signals are separated in a manner that the composite signal is switched by a square-wave subcarrier signal of 38 kHz derived from a pilot signal contained in the composite signal.
Since the square-wave subcarrier signal includes odd hamonics of fundamental 38 kHz signal, and it is used as a switching control signal, low pass filters (LPF) must be used so as to reduce the components of the higher hamonics contained in reproduced left and right signals (the output signals of switching cirucuit).
However, the utilization of low pass filters causes such problems as the deterioration of delay characteristic of composite signal and the reduction of amplitude of necessary range of composite signal, which result in the deterioration of separation characteristic, and an increase of distortion of the demodulated stereophonic signal.